Technical Field
The disclosure relates in general to a method for inspecting an article and an apparatus for measuring the same, and more particularly to a method for detecting an article by a multi-photon excitation technique and an apparatus of modified multi-photon fluorescence microscope for measuring the article.
Description of the Related Art
By doping various active materials within substrates or the matrix, various optical functions, including optical amplification, absorption, wavelength filtering, solid-state lighting and polarization distinction, can thus be performed. The followings are some examples. First, the laser crystal, formed by active-ion-doping into a bulk crystal, is the key element for optical amplification. For example, the Ti:Sapphire laser crystal is a sapphire (Al2O3) crystal doped with titanium ions. Second, for optical absorption and wavelength filtering, the absorptive filters or colored glass filters can be used, which are usually made from glass or plastics in which many absorptive active-ions have been added. These active ions transmit some wavelength components of light while attenuating others with extremely high absorption constants. For many filtering problems, these ion-doped wavelength filters are better choices than interference-type filters due to their much better wavelength extinction ratio. Third, in white organic light-emitting diodes (OLEDs), the low-gap dopants are dispersed deep inside the emissive layer. Through electrical pumping, visible wavelength components are radiated in the emissive layer. Finally, for the fabrication of polarizing plates which are key elements in liquid crystal displays, iodine-dyed ions added in the polyvinyl alcohol (PVA) polymer film(s) function as polarization-dependent light absorbers.
It is essential to monitor the spatial distribution and uniformity of dopants in the substrates or the matrix, such as laser crystals, color-glass filters, white OLEDs and polarizers mentioned above. The doped condition of the laser crystal is strongly related to the laser performance, including the threshold pumping power, slope efficiency and output power. When low-gap dopants are not uniformly dispersed in the emissive layer of OLED devices, this can lead to spatial variation in the color of the white electroluminescence, affecting lighting applications. The spatial distribution of doped iodine ions in PVA polymer films would be helpful for extracting and mapping more properties of a polarizer.
According to an analysis method of dopant spatial distributions or concentrations within the matrix known in the art requires a biopsy, including the removal (such as slicing), fixation, and staining of a piece sample from the object under test. The sliced samples are then put under a microscope to measure and analyze the image to show the relative concentrations of dopants. However, conventional analysis of dopant distribution or uniformity involves many time-consuming and complicated steps, for example, sample preparation and treatment and analysis steps. Also, the conventional slicing procedures are invasive, destructive, and time-consuming, such that the relative ion concentrations cannot be monitored quickly and in real time during fabrication process with high accuracy. Therefore, it would be desired for the researches to develop devices and methods for analysis of dopant distribution more simple and time-saving. Particularly, it is highly desired to develop a fast and biopsy-free method for analyzing a target material in the articles to be tested; for example, for quickly and accurately analyzing the doped ion concentration in an optical substrate (ex: a PVA film of a polarizer).
Two-photon fluorescence (TPF) microscope has been widely utilized in biological, chemical, and clinical applications. TPF processes usually involve fluorescent molecules with third-order nonlinearity, where two-excitation photons with equal energies are simultaneously absorbed by fluorescent molecules through the two-photon absorption (TPA) effect and one emission photon with a higher energy is generated. Molecular concentration imaging can thus be performed by measuring the intensities of higher-energy fluorescence photons, with a natural depth discrimination capability and high spatial resolutions in the focal plane. However, TPF microscope is not always suitable for monitoring the molecular concentration due to the non-radiative processes (i.e. non-fluorescent processes) that occur in some doped-ions or molecules when they are excited by TPA effects. Accordingly, for the doped-ions or molecules tending to occur the non-radiative processes, the doped-ions concentration would not be accurately determined by the conventional TPF microscopy.